Alveolar epithelial cells: differentiation and lung injury.

Re-epithelialization of alveolar epithelial cells is one of the important repair processes in many types of lung injury. The major functions of alveolar type II cells are synthesis and secretion of surfactant, hyperplasia in reaction to alveolar epithelial injury, and serving as progenitor cells for alveolar type I cells. The authors have examined the effects of several soluble factors on cultured alveolar type II cells in vitro, and also examined the histopathology and gene expression of surfactant proteins in the rat lungs with LPS, bleomycin and/or treated with keratinocyte growth factor. The authors next examined the effects of bone marrow stromal cells (BMSC) implanted transvenously into bleomycin-induced lungs. The authors found that keratinocyte growth factor (KGF) is a strong growth factor for alveolar type II cells, and that KGF instillation prevents bleomycin-induced lung injury. Furthermore, the authors showed the possibility of differentiation of implanted BMSC into alveolar epithelial cells. KGF and BMSC may play an important role in maintaining the alveolar epithelium and repairing the damaged epithelium after injury, and may well provide potential therapeutic alternatives.